The Theory of Plate Tectonics

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Vocabulary

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plates: a section of the lithosphere that slowly moves over the asthensophere, carrying pieces of continental crust
scientific theory: a well tested concept that explains a wide range of observations
plate tectonics: the geological theory that states that pieces of Earth's lithosphere are in constant, slow motion, driven by convection currents in the mantle
faults: breaks in Earth's crust where rocks have slipped past each other
transform boundary: the place where two plates slip past each other, moving in opposite directions
divergent boundary: the place where two plates move apart or diverge
rift valley: a deep valley caused by divergent boundaries
convergent boundaries: the place where two plates come together or converge

Outline

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Theory of Plate Motion

• canadian scientist named J. Tuzo Wilson
  • 1965 theory that cracks in the earth were actuallly the lithosphere broken into bits called plates
    • plates are in constant slow motion driven by convection currents in the mantle
      • convection current rises from mantle into the asthenosphere
      • no plate can budge without affecting the other plates surronding it

Plate Boundaries

• faults form along plate boundaries
  • each type of boundary has different plate movement

Transform Boundaries

• crust is neither created or destroyed at the transform boundary
  • earthquaked occur frequently along the transform boundary

Divergent Boundaries

• mostle occur at the mid-ocean ridge
  • rift valley forms along the divergent boundary

Convergent Boundaries

• result at this boundary is a collision or earthquake
  • collisions bring together the following: oceanic crust + oceanic crust, oceanic crust + continental crust, and continental crust + continental crust
    • oceanic crust is made mostly of basalt
    • continental crust is made mostly of granite

The Continents Slow Dance

• plates move from about 1- 10 cm a year
• 260 million years ago all the continents were joined together in a supercontinent called Pangaea
• 225 million years ago the supercontinent Pangaea began to break apart

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